1. Field of the Invention
The present invention relates to a conductive cap for covering an electronic element such as a piezoelectric element mounted on the upper surface of a substrate, an electronic component including such a conductive cap, and a method of forming an insulating film of the conductive cap.
2. Description of the Related Art
For conventional electronic component elements such as piezoelectric resonators or other suitable components, a package structure including a conductive cap has been used. Such a type of package structure will be described with reference to FIG. 6.
The package structure contains a substrate 51 having a rectangular sheet shape, made of an insulating material such as alumina, and a metallic cap 52. On the upper surface 51a of the substrate 51, terminal electrodes 53 and 54 for achieving external electric connection are provided. The terminal electrodes 53 and 54 each are extended onto the side surfaces, the end surfaces, and the lower surface, in addition to the upper surface 51a, so that the package structure can be surface-mounted onto a printed circuit board.
Further, a piezoelectric element is mounted onto the upper surface 51a of the substrate 51 by solder, a conductive bonding agent such as a conductive adhesive, or the like, though not shown in FIG. 6. The electrodes of the piezoelectric element are connected to the terminal electrodes 53 and 54, respectively.
For the purpose of sealing the piezoelectric element, a metallic cap 52 having an opening at the lower portion thereof is bonded to the substrate 51. A rectangular frame-shaped insulating film 55 is provided on the portion of the upper surface 51a of the substrate 51 that is arranged to be contacted with the end surface of the opening of the metallic cap 52. The insulating film 55 is formed by printing synthetic resin, or printing and baking glass. The thickness of the insulating film 55 is about 0.1 mm. Accordingly, the height of the chip electronic component to be produced can be reduced, even though the metallic cap 52 is used.
In recent years, it has been required to reduce the mounting areas of electronic components. With even greater miniaturization of components, it has been very difficult to print and form the insulating film 55 on the upper surface 51a of the substrate 51 with high precision.
Further, Japanese Unexamined Patent Application Publication No. 6-132762 discloses an electronic component 71 having a cap shown in FIG. 7. In this electronic component 71, terminal electrodes 73 and 74 each extends on the upper surface, the side surfaces, and lower surface of a substrate 72 made of an insulating material. A piezoelectric element 75 is bonded to the terminal electrodes 73 and 74 via solder members 76 and 77.
A metallic cap 78 is bonded to the upper surface of the substrate 72 by an insulating adhesive. In order to prevent the terminal electrodes 73 and 74 and the metallic cap 78 from short-circuiting, an insulating film 79 is disposed on the entire inner surface of the metallic cap 78.
In the prior art, no method of forming the insulating film 79 is specifically described. It is presumed that the insulating layer is precoated on a sheet material before the material is shaped into the metallic cap 78, and the precoated sheet material is formed to have the same shape as that of the cap.
When the metallic cap described in Japanese Unexamined Patent Application Publication No. 6-132762 is produced, the peripheral portion of the opening of the metallic cap 78 must be bent outward, as shown in FIG. 7, so that the insulating layer is always positioned on the portions of the terminal electrodes 73 and 74 to be contacted with the metallic cap 78. Accordingly, the process of producing the metallic cap 78 becomes complicated. Further, in some cases, when such bending work is carried out, the insulating layer 79 is peeled, making it impossible to reliably provide electrical insulation between the metallic cap 78 and the terminal electrodes 73 and 74.
In a chip electronic component in which an element such as a piezoelectric element or other electronic element is mounted onto a substrate, the piezoelectric vibration portion thereof is vibrated. As a result, the structure is such that the element is accommodated in a package that does not interfere with vibration of the element. After the element is mounted onto the surface of the substrate, a cap is fixed to the surface of the substrate to cover and seal the element.
FIG. 20 is a cross-sectional view showing an example of another conventional electronic component sealed with such a cap. In the conventional electronic component shown in FIG. 20, an insulating cap 30 is used. This is because the cap 30 is fixed to terminal electrodes 11 and 12 provided on a substrate 10 and must be insulative in order to prevent the terminal electrodes 11 and 12 from short-circuiting. An element such as a piezoelectric resonator is mounted onto the upper surface of the substrate 10. The element 20 is bonded to the terminal electrode 11 via solder 21 and the terminal electrode 12 with solder 22. A terminal electrode 13 is provided between the terminal electrodes 11 and 12 between the terminal electrodes 11 and 12 on the lower surface of the substrate 10 to produce a capacitor between the terminal electrodes 11, 12 and 13.
As the insulating cap 30, a ceramic cap, a resin cap, or other cap is used. However, these caps must have a thickness of 0.25 mm or larger because of the forming capabilities and limitations. Accordingly, it is not possible to reduce the height of the electronic component, and the area of the substrate becomes larger.
For the purpose of reducing the height of the electronic component and enhancing the integration density of the circuit board, it is preferable to use a metallic cap. However, if the metallic cap alone is fixed to the substrate, the terminal electrodes short-circuit, as described above.
In order to prevent the terminal electrodes from short-circuiting as described above, a method in which an insulating layer 31 is disposed on the substrate 10 and the terminal electrodes 11 and 12 onto which the metallic cap 32 is to be mounted, and the cap 31 is mounted onto the insulating layer 31, as shown in FIG. 21. In FIG. 21, elements such as a piezoelectric resonation element mounted onto the substrate 10 are omitted.
According to a method as described above, the metallic cap can be used. Thus, the height of an electronic component can be reduced. On the other hand, there arises the problem that with further miniaturization of the electronic component, it becomes more difficult to form the insulating layer on the substrate with high precision.
Japanese Unexamined Utility Model Application Publication No. 62-158828 and Japanese Unexamined Patent Application Publication No. 8-204491 disclose an electronic component provided with a metallic cap that is made of an aluminum sheet having an anodized film on the surface thereof. However, for the metallic cap, a sheet material is anodized. Therefore, in the case where the sheet material is formed into a cap shape, the end surfaces of the cap to be contacted with terminal electrodes on a substrate have no anodized films thereon. Accordingly, the terminal electrodes can not be prevented from short-circuiting.
Moreover, Japanese Unexamined Patent Application Publication No. 6-132762 discloses a metallic cap provided with an insulating layer disposed on the inner surface thereof. Such a metallic cap is shaped so that the end portions of the cap to be contacted with a substrate are bent outward, and the inner surface of the cap can be contacted with terminal electrodes. Accordingly, the insulating layer disposed on the inner surface is contacted with the terminal electrodes. Thus, the insulating layer is interposed between the metallic cap and the terminal electrodes, whereby the terminal electrodes can be prevented from short-circuiting.
In Japanese Unexamined Patent Application Publication No. 6-132762, a method of forming the insulating layer is not specifically described. It is presumed that the insulating layer is precoated on a sheet material before the material is formed in the metallic cap shape, and the precoated sheet material is formed into the cap shape. In the case of such a metallic cap, the end portions of the cap are bent outward so that the insulating layer on the end portions of the cap is positioned on the portions of the cap to be contacted with the terminal electrodes. Further, during bending, the insulating layer may be peeled so that the insulating properties become insufficient.
In some cases, it is necessary to provide an insulating layer for the outer surface of the metallic cap, so that insulation between the electronic component and other elements is maintained when the electronic component is mounted onto a circuit board. In Japanese Unexamined Patent Application Publication No. 6-132762, only a method of forming the insulating layer on the inner surface of the cap is disclosed.
In order to overcome the problems described above, preferred embodiments of the present invention provide a conductive cap that is adapted to be insulated from terminal electrodes on a substrate electrically and securely, is produced in a simple process, and reduces the size and height of an electronic component attributed to the conductive cap included in the component. Preferred embodiments of the present invention also provide an electronic component containing the conductive cap, and a method of forming an insulating film of the conductive cap.
According to a preferred embodiment of the present invention, a conductive cap for use in an electronic component including an opening at the lower portion thereof, and being adapted to be fixed to the upper surface of the substrate of the electronic component on the opening side of the cap so as to cover at least an electronic component element mounted on the upper surface of the substrate having terminal electrodes provided thereon, wherein the end surface of the opening and the inner and outer side surfaces thereof in connection to and in the vicinity of the end surface are provided with an insulating film disposed thereon.
The insulation resistance between the opening end surface of the conductive cap and the outer side of the insulation film may be at least about 109 xcexa9.
The thickness of said insulating film may be in the range of about 4 xcexcm to about 25 xcexcm.
Preferably, when the opening end surface of the conductive cap and its adjacent portion thereof are viewed in a section taken perpendicularly relative to the circumferential direction of the conductive cap, the opening end surface of the cap and the inner side surface thereof in connection to the opening end surface define a curved line, and the radius R of curvature of the curved line is in the range of about 80 xcexcm to about 150 xcexcm.
According to another preferred embodiment of the present invention, an electronic component includes a substrate having a plurality of terminal electrodes provided at least on the upper surface thereof, an electronic component element fixed to the substrate and electrically connected to the plurality of terminal electrodes, and a conductive cap having an opening at the lower portion thereof, provided with an insulating film disposed on the opening end surface thereof and its vicinity and bonded to the substrate on the opening side thereof.
In the electronic component, the electronic component element may be a piezoelectric element or other suitable electronic component.
Further, in the electronic component, the conductive cap may be a metallic cap.
According to a preferred embodiment of the present invention, a method of forming an insulating film of a conductive cap includes the steps of holding a plurality of conductive caps each having an opening at the lower portion thereof while the conductive caps are arranged by a holding device, pressing the opening end surface of the plurality of conductive caps held by the holding device against a resin layer for forming an insulating film having a predetermined thickness, separating the conductive caps from the resin layer for forming an insulating film, whereby the insulating film is formed on the opening end surface of each conductive cap and its vicinity of the opening end surface by the transfer method, and drying the insulating film after the transfer step.
In the method, as the resin for forming an insulating film, a resin having a viscosity at about 25xc2x15xc2x0 C. of about 5000 to about 20000 cps may preferably be used.
According to another preferred embodiment of the present invention, a method of forming an insulating film of a conductive cap for sealing an electronic component includes the steps of providing a conductive cap that is adapted to be fixed to the surface of a substrate having terminal electrodes disposed thereon so as to cover and seal an element mounted to the surface of the substrate, the insulating film being adapted to electrically insulate the terminal electrodes from the metallic cap, wherein the conductive cap is made of aluminum or an alloy thereof, and forming an insulating film on the surface of the conductive cap by anodization carried out in the cap-shaped state.
As described above, the anodization is carried out in the cap-shaped state. Accordingly, the insulating film can be formed by the anodization on the surface portions of the conductive cap to be contacted with the terminal electrodes when the conductive cap is fixed to the surface of the substrate. Hence, such a metallic cap alone can be fixed to the surface of the substrate by an adhesive or other joining material or element to achieve sealing.
The anodization can be performed under the general anodization conditions. An oxidized film can be electrolytically formed on the metallic cap so as to define an anode. As an electrolyte, generally-used acidic electrolytes such as sulfuric acid, oxalic acid, chromic acid, and so forth may be preferably used.
Preferably, the anodization is carried out while the conductive cap is held by a jig and is electrically connected. As the jig, a conductive jig is preferably used, and is electrically connected to the metallic cap. The conductive cap as an anode is electrolytically treated. This method is suitable in the case where the conductive caps are individually separated and are separate from each other.
Preferably, the anodization is carried out while the conductive caps are connected to each other in a hoop-shape state. In the hoop-shape state, a sheet material and the caps are partially connected to each other after the sheet material is punched and shaped into caps.
In such a hoop-shape state, the anodization can be continuously carried out. That is, for the continuous anodization, the hoop wound around one roll or the like is unwound and fed into an anodization bath, and after the anodization, is taken up around the other roll. In this case, the electrical conduction state of the hoop can be kept by moving a contact for electrically connecting the hoop correspondingly to the movement of the hoop.
Further, the hoop cut to a predetermined unit length may be dipped into an anodization bath to be anodization-treated. In this case, by utilizing a piece for holding each cut hoop as a contact, the cut hoop can be electrically connected.
Further, according to another preferred embodiment of the present invention, there is provided a conductive cap for sealing an electronic component, the cap being adapted to be fixed to the surface of the substrate of the electronic component so as to cover and seal an element mounted onto the surface of the substrate having terminal electrodes disposed thereon, wherein the conductive cap is made of aluminum or an alloy thereof, and an insulating film is formed by anodization at least on the surface portions of the conductive cap to be contacted with the terminal electrodes.
The conductive cap of various preferred embodiments of the present invention can be produced according to the method of forming an insulating film of another preferred embodiment of the present invention. The conductive cap of various preferred embodiments of the present invention alone can be fixed to the surface of the substrate by an adhesive or other joining material or element, since the insulating film is formed at least on the surface portions of the conductive cap to be contacted with the terminal electrodes, thereby securing the insulation between the terminal electrodes on the substrate and the conductive cap. Thus, an electronic component having a greatly reduced height is efficiently produced.
According to another preferred embodiment of the present invention, a method of forming an insulating film of a conductive cap for sealing an electronic component, which is fixed to the surface of the substrate of the electronic component having terminal electrodes disposed thereon so as to cover and seal an element mounted onto the surface of the substrate, the insulating film being adapted to electrically insulate the terminal electrodes from the conductive cap, wherein the insulating film is formed on the surface of the conductive cap by electrodeposition coating.
According to this preferred embodiment of the present invention, the insulating film can be formed in the cap-shaped state. Accordingly, for any cap-shape, the insulating film can be formed on the surface of the portions of the conductive cap to be contacted with the terminal electrodes when the conductive cap is fixed to the surface of the substrate. The conductive cap alone can be fixed to the surface of the substrate by an adhesive or other joining material or element to achieve sealing.
As the electrodeposition according another preferred embodiment of the present invention, a conventional generally-used electrodeposition coating method can be adopted. The electrodeposition coating can be performed by use of acationic or anionic electrodeposition coating material and by setting the conductive cap as a cathode or anode.
Preferably, a conductive double side adhesion tape is bonded to a conductive supporting sheet, and the metallic cap is bonded to the conductive double side adhesion tape, electrically connected, supported, and electrodeposition-coated. According to this method, many conductive caps can be simultaneously bonded to the double side adhesion tape to be supported and fixed. Thus, many metallic caps can be electrodeposition coated simultaneously and efficiently.
Also preferably, the electrodeposition-coating is carried out while the conductive cap is supported by a jig, and electrically connected. According to this method, the cap can be held and fixed by the simple jig.
According to a further preferred embodiment of the present invention, there is provided a conductive cap for sealing an electronic component, which is fixed to the surface of the substrate of the electronic component having terminal electrodes disposed thereon so as to cover and seal an element mounted onto the surface of the substrate, wherein an insulating film is formed at least on the portions of the conductive cap to be contacted with the terminal electrodes by electrodeposition coating.
Other features, characteristics, elements and advantages of the present invention will become apparent from the following description of preferred embodiments thereof with reference to the attached drawings.